Semi-conductor product and method for making same



June 13, i 967 J, E. ALLEF'GRETTI 3,325,314

SEMI-CONDUCTOR PRODUCT AND METHOD FOR MAKING SAME Original Filed Oct.27, 1961 2 Sheets-Sheet 1 'Tlcil.

INVENTCSR JOHN E.ALLEGRETTI ATTORNE June 13, 967 J. E. ALLEGRETTI3,325,314

SEMI-CONDUCTOR PRODUCT AND METHOD FOR MAKING SAME Original Filed Oct.2'7, 1961 2 Sheets-Sheet 2 INVENTOR JOH E. ALLEGRETTI United StatesPatent 3,325,314 SEMI-CONDUCTOR PRODUCT AND MUETHOD FOR MAKING SAME JohnE. Allegrctti, East Brunswick, NJ, assignor to Siemens & HalslreAktiengesellschaft, Berlin and Munich, Germany, a corporation of GermanyContinuation of application Ser. No. 148,253, Oct. 27, 1961. Thisapplication Aug. 27, 1965, Ser. No. 497,581 4 Claims. (Cl. l48--1'75)This invention is a continuation of my copending application Ser. No.148,253 filed Oct. 27, 1961, now abandoned, and relates to singlecrystal silicon semiconductor bodies grown from the vapor phase bythermal decomposition and, more particularly, it relates to a method ofgrowth of silicon semiconductor layers having a flat, imperfection-freesurface.

The process of deposition of silicon semiconductor material and activeimpurities therewith onto a single crystal silicon semiconductorsubstrate from the vapor phase by simultaneous thermal decomposition ofa silicon compound and active impurity compounds therewith in thepresence of hydrogen is well known in the art. What is found is thatthermal decomposition of silicon under these conditions producessurfaces with one or more surface imperfections. For example, thesurface may exhibit pyramidal growth, both rectangular and triangular inshape. Other imperfections manifest themselves in the form of pittingand growth stops wherein small hillocks are present on the surface, oras thickness deformities which occur in the form of a coarse texture orshingle appearance on the surface. As will be apparent to others skilledin the art, the availability or vapor-grown, flat, imperfection-free,single crystal semiconductor surfaces would enable the fabrication ofsemiconductor devices of improved quality.

An object of this invention is to provide a single crystal siliconsemiconductor body including a plurality of layers of single crystalsilicon semiconductor material of different conductivity separated by atransition region wherein said body has a flat, imperfection-freesurface.

Still another object of the instant invention is to provide a singlecrystal silicon semiconductor body by growth from the vapor phase havinga surface layer which has a substantially improved surface quality, bygrowth onto a single crystal silicon semiconductor substrate having apredetermined crystal orientation.

Among the other objects of the invention is to provide a method ofmaking such bodies by thermal decomposition from the vapor phase.

These and other objects will be made apparent from the following moredetailed description of the invention, in which reference will be madeto the accompanying drawings, in which:

FIGURE 1 is a photolithographic reproduction of the surfacecharacteristics of a single crystal silicon semiconductor layer formedby growth from the vapor phase; and regions marked A illustrate theimperfection-free surfaces produced according to the present invention,whereas those designated as B and C are indicative of thecharacteristics of surfaces produced in the prior art;

FIGURE 2 is a more detailed view of region B;

FIGURE 3 shows regions A and C under high magnification;

FIGURE 4 is an interference pattern of regions A and C;

FIGURE 5 is a schematic illustration, in section, of a siliconsemiconductor substrate oriented in accordance with the presentinvention; and

FIGURE 6 shows a manner of preparing oriented sub strates in accordancewith the invention starting with a single crystal of semiconductormaterial.

In accordance with the present invention there is provided a singlecrystal silicon semiconductor body including a plurality of layers ofsingle crystal semiconductor material, and wherein the surface layer ofthe body has a substantially improved surface quality. The semiconductorbodies produced herein have surfaces which are exceedingly fiat andimperfection-free. In a preferred form of the present invention, singlecrystal semiconductor bodies having such improved surface qualities areprepared by thermal decomposition from the vapor phase onto a singlecrystal silicon semiconductor substrate which is oriented in a preferredmanner. In particular, in the present invention, a silicon substrate isoriented at least three-eighths of a degree and not more than fivedegrees off orientation from a low order Miller Indices growth plane. Ina specific embodiment of the invention, silicon semiconductor bodieshaving fiat, imperfectionfree surfaces are produced by orienting thesubstrate in the aforementioned predetermined amount off orientation inthe [111] plane of the crystal along a [211] 211 direction.

As another feature of the present invention there is provided a methodof making such silicon semiconductor bodies having these improvedsurface qualities by growth from the vapor phase. In accordance withthis method, growth from the vapor phase is effected by thermaldecomposition of a semiconductor material and active impuritiestherewith in the presence of hydrogen onto a silicon semiconductorsubstrate oriented in a predetermined manner at deposition temperaturesin the range of 1150-1200 C.

The process of growth from the vapor phase employed in the formation ofsemiconductor bodies in accordance with the invention utilizes knownthermal semiconductor materials with the only criterion being that adecomposable vapor source of the material be available. The termsthermally decomposable, thermal decomposition and the associated depositof a product. of decomposition, as used herein, are intended to begeneric to the mechanisms of heat-cracking as, for example, thedecomposition of silicochloroform or silicon tetrachloride andliberation of silicon atoms through the mechanism of high temperaturereactions wherein the high temperature causes interaction betweenvarious materials with liberation of specific materials or atoms as, forexample, the reaction of silicochloroform and hydrogen:

used in the preferred embodiments of this invention as hereinafterindicated.

Single crystalline silicon semiconductor bodies in accordance with theinvention may he formed, in general, utilizing the apparatus andtechniques described in the teachings of patent application SN. 86,239by Benzing, Krsek and Topas, filed Jan. 31, 1961, and now Patent No.3,131,098. As is disclosed in the Benzing et a1. application,semiconductor material is deposited upon a heated essentially singlecrystal semiconductor starting element from a decomposable sourcethereof in a reaction chamber. After a predetermined period of timeduring which the desired thickness of semiconductor material has beendeposited, the reaction chamber is flushed with a gas to remove unwantedatoms of active impurity therefrom. Thereafter, additional semiconductordecomposable source material and atoms of active impurity of a desiredtype and degree are introduced into the reaction chamber and anadditional layer of desired thickness of semiconductor material isdeposited in essentially single crystalline form contiguous with thelayer of material previously deposited. This process may be continueduntil such a time as the desired numbers of layers of semiconductormaterial of alternating conductivity type or degree, each having ajunction separating it from the adjacent layer, are formed. As isevident, any desired number of layers of material, and any desirednumber of junctions, may be formed in accordance with any given designconsiderations.

Referring now to FIGURE 1, there is shown an actual photolithographicreproduction of the surface of a single crystal silicon layer formed bythermal decomposition of silicochloroform and hydrogen at 1150-1200 C.onto a single crystal silicon substrate oriented in a predeterminedmanner. In particular, the substrate is formed by providing a 4 arc ofcurvature from a [111] plane of the crystal, thereby exposing a numberof crystal planes which are close to a [111] plane. In this manner, itis possible to illustrate in a single experiment the characteristics oflayers formed on different substrate crystal planes. As may be seen inthe drawing, certain regions contain surface imperfectionscharacteristic of those surfaces previously obtained in the art. On theother hand, other regions exhibit a surface which is substantiallyimperfection-free. It is the latter surfaces which are characteristic ofthose produced according to the present invention and which are sodramatically to be distinguished from those produced in the past.

As may be observed, the region marked A in FIGURE 1 is essentially clearand free of any undesirable surface imperfections. The regions marked Band C, however, have one or more surface imperfections. Region B, forexample, is illustrative of a pyramidal growth imperfection. FIGURE 2shows this type of growth in more detail. Region C contains a form ofsurface imperfection called hillock-ty pe growth. FIGURE 3 shows regionC under high magnification.

In FIGURE 4 there is shown the interference pattern, characteristic ofregions A and C, under optical examination. What is shown therein isthat the surface layer in region A is substantially free of distortinginterference patterns, which indicates that the region is free ofsurface imperfections. Stated in more mathematical terms, region A hasless than one interference line across 20 mm. of the surface thereof.Region C, on the other hand, has very many such lines in the samelength.

The desired type of surface quality exhibited in region A occurs on thatportion of the silicon crystal which is oriented at least /8 of a degreeand not more than 5 off orientation from a [111] plane in the 211direction of the crystal. Single crystal silicon semiconductorsubstrates which are oriented in this manner, have on an atomic scale, anumber of atoms of semiconductor material arranged in the form of steps.This stepwise arrangement exposes a large number of atomic layers of thematerial, as illustrated in FIGURE 5. In a given length of exposedsurface there are a number of exposed atomic layers, the exact numbervarying with the extent to which the crystal is oriented off from a lowMiller indices crystal plane. For example, if the silicon crystal isoriented of a degree off orientation there are 1.42 atomic layersexposed per centimeter of length of the crystal. At a preferred 1.5 offorientation from the [111] plane, there are 4.9x 10 such exposed atomiclayers, and at 5 there are 1.9 10 exposed atomic layers. In order toachieve the desired imperfection-free growth it is necessary that thenumber of exposed atomic layers be within the limits enumerated above.

FIGURE 6 illustrates a manner of preparation of a suitably orientedsilicon single crystal substrate 10 in accordance with the invention. Acut along the lines 11- 12 is made in the single crystal body in themanner shown at an angle 0, thereby exposing a surface 13. The cut ismade 0 degrees off [111] orientation in the '2 11 direction of thecrystal.

What has been described is a method for producing single crystal siliconsemiconductor bodies having improved surface qualities. In a preferredform of the invention a silicon crystal substrate is provided which isoriented at least of a degree and not more than five degrees offorientation from a [111] plane of the crystal in the 11 direction. Thena layer of silicon is deposited thereon by thermally decomposingsilicochloroform and hydrogen at 1l501200C. The layer thus formed has aclear, flat and substantially imperfectionfree surface and the sameorientation as that of the substrate.

While the invention has been described with particular reference to theformation of an individual semiconductor body having improved surfacequalities, it will be understood that a plurality of such bodies may beformed simultaneously. Within the temperature ranges specified herein, aplurality of such bodies may be formed without appreciable diffusion ofimpurities from one body to another during the deposition process.

I claim:

1. A method for epitaxial depositing monocrystalline silicon from thegaseous phase onto a heated substrate which comprises epitaxiallyvapor-depositing monocrystalline silicon at least primarily on a flatdeposition surface which departs at least /8 of a degree and not morethan 5 degrees off orientation from a [111] plane of the crystal in thell direction.

2. A single crystal silicon semiconductor body comprising a substrate ofsingle crystal silicon semiconductor material of predeterminedconductivity oriented at least of a degree and not more than 5 degreesoff orientation from a [111] plane of the crystal in the 11 directionand a single crystal silicon semiconductor material, of conductivitydifferent from that of said substrate layer, vapor-deposited by thermaldecomposition on said substrate layer, said vapor-deposited layershaving a clear, flat, substantially imperfection-free surface and havingthe same orientation as the substrate.

3. A single crystal silicon semiconductor body comprising a substrate ofsingle crystal silicon semiconductor material of predeterminedconductivity oriented at least /8 of a degree and not more than 5degrees off orientation from a [111] plane of the crystal in the 11direction and a single crystal silicon semiconductor material, ofconductivity different from that of said substrate layer, formed bythermal decomposition from the vapor phase on said substrate layer, saidvapor-deposited layers having a clear, flat substantiallyimperfection-free surface characterized by having less than oneinterference line per 20 mm. of length across said surface and havingthe same orientation as the substrate.

4. A single crystal silicon semiconductor body comprising a substrate ofsingle crystal silicon semiconductor material doped to one conductivityoriented at least of a degree and not more than five degrees offorientation from a low Miller indices plane, the highest Miller indexnot exceeding 2, and a single crystal silicon semiconductor material ofconductivity different from that of said substrate layer vapor-depositedby thermal decomposition on said substrate layer, said vapor-depositedlayers having a clear, flat, substantially imperfection-free surface andhavin gthe same orientation as the substrate.

1. A METHOD FOR EPITAXIAL DEPOSITING MONOCRYSTALLINE SILICON FROM THEGASEOUS PHASE ONTO A HEATED SUBSTRATE WHICH COMPRISES EPITAXIALLYVAPOR-DEPOSITING MONOCRYSTALLINE SILICON AT LEAST PRIMARILY ON A FLATDEPOSITION SURFACE WHICH DEPARTS AT LEAST 3/8 OF A DEGREE AND NOT MORETHAN 5 DEGRES OFF ORIENTATION FROM A (111) PLANE OF THE CRYSTAL IN THE<211> DIRECTION.